1. Field of the Invention
The present invention relates to a TE01xcex4-mode dielectric resonator having a resonator section and a supporting base section which are made of the same dielectric material as a single unit; a filter, a duplexer, and an oscillator each using the dielectric resonator; and a communication apparatus using the above.
2. Description of the Related Art
Generally, dielectric resonators of the aforementioned type have a structure in which a supporting base having a low dielectric constant is adhered to a resonator section having a high dielectric constant. In this case, however, a problem is that adhering work for the supporting base section is required, and manufacturing costs are increased thereby.
In this situation, there is proposed a dielectric resonator having a resonator section and a supporting base section that are formed of the same dielectric material as a single unit (Japanese Unexamined Patent Application Publication No. 8-222917). In the dielectric resonator according to Japanese Unexamined Patent Application Publication No. 8-222917, the supporting base section is formed in the shape of a cylinder with an outside diameter smaller than that of the resonator section. A radial slit is provided in the supporting base section, a groove is provided in an outer peripheral face, and a through-hole is provided in the diameter direction to eliminate a part of the supporting base section, thereby reducing the effective dielectric constant of the supporting base section so as to minimize reduction in the unloaded Q value. Thus, to prevent the reduction in the unloaded Q value of the TE01xcex4-mode dielectric resonator that includes the supporting base, formed as a single unit, it is important to reduce the amount of dielectric in the supporting base section, thereby reducing the dielectric constant of the supporting base section.
The dielectric resonator as described above is immobilized with an adhesive or the like onto either a substrate or a bottom wall of a cavity so that the bottom end face of the supporting base section is used as a mounting face. It is used either in a filter or a transmitting device.
In the above-described conventional single unit dielectric resonator that includes the supporting base, however, there is a right-angled step portion at the border between the resonator section and the supporting base section. Since the border area is not pressed evenly during press forming, the formation density (the density of the formed body) sharply varies at the border area. Also, since the shape of the supporting base section is complicated, problems are raised in that stable formation is impossible, and formation using a uniaxial pressuring press is difficult or impossible. Other problems are raised by the complicated shape of the forming die. Therefore, manufacturing costs therefor are high, and the service life thereof is short.
Also, in the above-described dielectric resonator, since the outside diameter of the supporting base section is smaller than that of the resonator section, problems are raised in that the dielectric resonator cannot be stably mounted in a cavity by automatic mounting.
To overcome the above described problems, embodiments of the present invention provide a dielectric resonator that is cheap, that has good characteristics, that allows the unloaded Q value to be minimized, that can be easily formed, and that can be stably mounted; and a filter, a duplexer, an oscillator, and a communication apparatus that use the dielectric resonator.
One embodiment of the present invention provides a dielectric resonator comprising a resonator section and a supporting base section which are made of the same dielectric material as a single unit; wherein said resonator section and said supporting base section have substantially the same outside diameter; a concave section the cross section of which is a trapezoidal shape is provided within said supporting base section such that the inside diameter of said supporting base section is generally tapered from the end face, which is used as a mounting face, in the direction toward said resonator section.
Of course, the cross section of the concave portion need not be precisely trapezoidal. Skilled persons will appreciate that other generally tapered cross-sectional shapes are usable as well.
According to the above structure and arrangement, the mounting face of the supporting base section is ring-shaped, and the width thereof (in other words, the thickness of the dielectric constituting the supporting base section) is reduced. Therefore, the effective dielectric constant of the supporting base section is significantly reduced. This minimizes reduction in the unloaded Q value of the resonator.
Further, the dielectric resonator has a simple shape, since only the above-mentioned concave trapezoidal cross section is formed in the supporting base section, and no right-angled step section is formed. Therefore, sharp variations in the formation density of the formed body are substantially avoided. Therefore, the dielectric resonator does not become deformed and reduced in mechanical strength and can be easily formed by the use of a low-cost forming method using a uniaxial-pressuring press. Starting with the reduced width of the ring shape at the mounting face of the supporting base section, the thickness of the dielectric constituting the supporting base section becomes greater in the direction toward the resonator section. This prevents reduction in the mechanical strength of the formed body.
Also, since the outside diameter of the supporting base section is the same as that of the resonator section, the dielectric resonator can be stably mounted.
In the above described dielectric resonator, a through-hole may be provided in a central portion of the resonator section and continuing into the concave section. This arrangement is particularly applicable when the dielectric resonator is immobilized within a cavity with an adhesive. Air that is hermetically enclosed in the concave section can expand due to high temperatures that occur in the curing process. This trapped air can cause positional deviations after adhesion. This problem is avoided by providing the hole in the resonator section.
Further, a filter, a duplexer, and an oscillator may be provided with the above described dielectric resonator. Thereby, manufacturing costs can be reduced, and good characteristics thereof can be obtained.
Further, a communication apparatus may be provided with one of the above described filter, duplexer, and oscillator. Thereby, a communication apparatus with a good characteristics can be obtained cheaply.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.